slightly more complex, transmitting a signal
to the remote control room, where the measurements can be read or recorded.
Controllers: There are three basic types of controllers 1) digital (e.g. microprocessor or computer based,
2) analog, and 3) pneumatic. The following guidelines maybe applied in selecting
the appropriate controller • For plants with many control loops use digital type of controllers.
• For the expansion of existing controls within a plant use the existing technology. This maybe either digital,
analog electronic, or pneumatic controllers.
• Use pneumatic controllers in hazardous areas.
• Avoid use of pneumatic controllers in the control room.
• When using digital control avoid depending on a single or a few control devices for the entire plant without having a backup. A redundant controller might not be required if only a single controller controls one loop. However, if a single controller controls a large number of loops then provide redundancy so that if the controller fails another controller will automatically takeover Use the type of controller that is the most economical and reliable.
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